1. Technical Field
The present disclosure relates to a communications device having relays and more specifically, to a communications device having relays that allow the communications device to conduct communications via the relays even if a power failure occurs.
2. Description of the Related Art
As industrial Ethernet technology is less costly, has high efficiency and is convenient to maintain, more and more applications can be found in the industrial fields in place of field buses. Such Ethernet may be connected in a ring, a line, etc. The ring connection is advantageous in that it has simple connection and saves cost, and thus is frequently used.
FIG. 1 is a block diagram of an existing daisy chain communications device.
As shown in FIG. 1, the communications device includes a master unit 10, first to fourth slave units 20, 30, 40 and 50. The slave units are connected to one another so that they can communicate via first and second ports P1 and P2 of each of the slave units. In addition, the slave units include communications processors 22, 32, 42 and 52, respectively, to process commands or data received from the master unit 10. With this configuration, the first to fourth slave units 20, 30, 40 and 50 may be controlled by the single master unit 10 by using minimal lines to communicate with one another. Each of the slave units may include a power module therein to receive power. For example, an inverter may be included.
If power failure occurs in one of the slave units, e.g., the second slave unit as shown in FIG. 2, the slave unit and the subsequent slave units cannot conduct communications any more.
For example, power supplied to the second slave unit 30 is interrupted, the second slave unit 30 cannot conduct communications. Additionally, in the communications device with the configuration shown in FIG. 2, the third slave unit 40 and the fourth slave unit 50 cannot communicate with others, either after the failure has occurred in the second slave unit 30.
To solve such problem, it may be contemplated to connect a cable that supplies power directly to a slave unit, i.e., duplex power to the communications device. This approach, however, may increase installation cost and time, and unexpected difficulty may take place due to many power cables. In addition, a lot of effort may be required for maintenance.